1. Field of Invention
This invention relates to methods and systems for image rendering using digital halftoning.
2. Description of Related Art
Because various image rendering systems, such as copiers and printers, are not suited to directly reproduce the variety of intensity levels present in a continuous tone (contone) image, digital halftoning techniques are used to render intensity or lightness levels, by converting the continuous tone image to a halftone image. A halftone representation is an approximation of an original image that uses a series of carefully placed dots of various sizes and/or patterns that, when viewed from a distance, creates an illusion of continuous tones.
Generally, the dot area or halftone screen size is desirably small to create the illusion of a continuous tone. However, if the screen size is too small, various image artifacts, such as false contours, appear in the halftone image that do not exist in the original continuous tone image.
If the screen size of a rendering system is increased, the rendering system can produce more gray levels that better represent smoothly varying regions. However, increasing the screen size results in a coarser halftone screen which is less able to represent fine details of the original image. Since a halftone screen cannot simultaneously be both very large and very small, a rendering system must choose between screens of varying sizes according to the image characteristics of the image to be reproduced. However, storing various screens for a variety of screen sizes and types can use a significant amount of memory.